London attack: what we know so far

A massive police operation is under way after a terrorist attack on Wednesday in Westminster, in the heart of London.

This is what we know so far:

* Five people have died - police officer Keith Palmer, 48, mother-of-two Aysha Frade and US tourist Kurt Cochran. A 75-year-old man died in hospital on Thursday night after his life support was withdrawn. The attacker, Khalid Masood, also died.

* Masood, 52, had a string of criminal convictions including possession of a knife but he was not the subject of any current investigations and there was "no prior intelligence about his intent to mount a terrorist attack".

* Eight people have been arrested and a number of addresses raided across London, Birmingham and elsewhere.

* Those arrested include a 39-year-old woman held at an address in east London on suspicion of preparation of terrorist acts.

* A 21-year-old woman and a 23-year-old man were also arrested at an address in Birmingham on suspicion of preparation of terrorist acts.